Method for decreasing the cyclic oligomer content in polyester product

ABSTRACT

The present invention relates to a method for decreasing the cyclic oligomer content in polyester product; during the manufacturing process of polyethylene terephthalate, adding at least one selected from the group consisting of calcium phosphate having Ca 3 (PO 4 ) 2  or Ca 5 OH(PO 4 ) 3  structure and of carboxy phosphonic acid having a structure (1) as follows:  
                 
 
     wherein R 1 , R 2 , and R 3  are alkyls or hydrogen atoms, R is an alkyl;  
     whereby not only is the production of cyclic oligomer in ester chips effectively restrained, but also the cyclic oligomer regenerated in the rear-stage melting process is decreased.

BACKGROUNG OF THE INVENTION

[0001] 1. Field of this Invention

[0002] The present invention relates to a method for decreasing thecyclic oligomer content in polyester product, which improves the methoddisclosed on the U.S. Pat. No. 6,392,005 issued to the applicant, byadding other chemicals during the production or manufacturing process ofpolyethylene terephthalate to further effectively restrain the cyclicoligomer residuals in polyethylene terephthalate chips and decrease theamount of regenerated cyclic oligomer at the rear-stage melting process.The aforementioned polyethylene terephthalate is capably made intoproducts such as polyester bottle, fiber, film, and laminate throughdifferent manufacturing processes.

[0003] 2. Description of Prior Art

[0004] Polyethylene terephthalate (PET) is well known as a heatplasticized plastic material having good physical characters and acapability of being recycled, so it is widely used in manufacturingproducts such as polyester bottles, polyester fiber, polyester films,and polyester laminates, which makes it a valuable plastic material.

[0005] However, during the process of manufacturing PET, some cyclicoligomers having low molecular weight, particularly those with whitecrystallized powder, are produced from side reaction. This sort ofoligomer has a melting point of above 300° C. to pollute the mold whileprocessed and further adhere to polyester bottles; consequently, theproduction line needs to be shut down and cleaned from time to time.Moreover, during the high temperature heat crystallization process ofmanufacturing the PET into a heat-filling resistance bottle, in whichthe temperature of both the crystallization and the heat-filling isabove 80° C., most of the residual cyclic oligomer in PET or the cyclicoligomer regenerated during processing may transfer to the surface oreven enter into packaged content to hazard human health

[0006] To solve said cyclic oligomer problems, we disclose, in U.S. Pat.No. 6,392,005, adding, during the melting process of PET, a compound(hereinafter called PI) containing phosphorus with the followingstructure:

[0007] in an amount of 50˜3000 ppm based on the weight of PET toeffectively decrease the cyclic oligomer content of PET chips and theirprocessed product.

[0008] Japan publication No. 12-219731 discloses that adding SO₃Xcompound effectively restrains the produced cyclic oligomer content inthe melted state polymerized PET.

[0009] Japan publication No. 12-204229 discloses that adding alkalimetals or alkaline-earth metals such as calcium acetate or magnesiumbenzoate into the PET containing germanium catalyst can effectivelyrestrain the cyclic oligomer content.

[0010] Japan publication No. 12-219729 discloses that while each mole ofPET contains 0.5×10⁻⁴˜4×10⁻⁴ moles of antimony element and 1×10⁻⁴˜5×10⁻⁴moles of phosphoric acid, wherein the mole ratio of antimony element tophosphorus element is 1˜3, the cyclic oligomer content is effectivelyrestrained.

[0011] Japan publication No. 12-198937 discloses that while thegermanium element is 0.5×10⁻⁴˜4×10⁻⁴ moles relative to the acidcomponent of PET, the phosphoric acid is added until the phosphoruselement is 1×10⁻⁴˜7×10⁻⁴ moles relative to the acid component of PET,wherein the mole ratio of germanium element to phosphorus element isgreater than 1.6, to effectively restrain the cyclic oligomer content.

[0012] Japan publication No. 12-80284 discloses that PET chips proceedsmelt blending with heat plasticized resin masterbatch which contains oneof the following three structural compounds: alkylene oxide, orpolyalkylene glycol, or bisphenol. The analyzed cyclic oligomer contentof the resin is lower than that of the PET obtained from the processwithout said compounds.

[0013] Japan publication No. 11-80520 discloses that the situation ofpollution on mold during blow-molding is improved while the amidecompound is added into solid state polymerized PET.

[0014] Japan publication No. 10-168168 discloses a process of producingthe PET chips containing 2˜4 wt % of diethylene glycol by using anamorphous state germanium dioxide as catalyst. The time point of theaddition of amorphous state germanium dioxide catalyst is while theesterification ratio reaches above 90% to reduce the production offormaldehyde, acetaldehyde, and cyclic oligomer while inject-molded.

[0015] Japan publication No. 10-110026 discloses that the addition ofalkaline metals and alkaline earth metals such as lithium acetic,calcium acetic can restrain the cyclic oligomer content of ester chipsand bottles thereof.

[0016] Japan publication No. 9-221540 discloses that while the DEGcontent of PET chips is 1˜4 mole %, and the intrinsic viscosity is0.60˜0.90 dl/g, and the phosphoric acid content based on the weight ofPET is 5˜25 ppm, and the content of germanium element based on theweight of PET is 20˜60 ppm, and the mole ratio of germanium elementcontent to phosphorus element content is between 0.4˜1.5, said polyesterhas low cyclic oligomer content.

[0017] Japan publication No. 9-296029 discloses that for the PETcontaining germanium catalyst, while the alkaline-earth metal atomcontent based on PET is 1×10⁻⁴˜5×10⁻³ moles, the cyclic oligomer contentin PET is low and the regenerated cyclic trimer from melting process islittle.

[0018] Japan publication No. 59-25815, 3-174441, 6-234834, and 347830disclose a specific process that PET is treated by boiling water, bywhich the residual cyclic oligomer in PET chips and the regeneratedcyclic oligomer during processing can be reduced.

[0019] U.S. Pat. No. 6,020,421 discloses a PET composition containing ametal atom A and a phosphide containing a valance of 5, wherein themetal atom A can be antimony atom, titanium atom, or germanium atom, andthe phosphide can be selected from the phosphate group consisting oforthophosphoric acid salt, metaphosphoric acid salt, polymetaphosphoricacid salt (HPO₃)_(m) (m≧3), and polyphosphoric acid Hn+2PnO₃n+1 (n≧2).

[0020] U.S. Pat. No. 5,948,458 discloses the addition of phosphate intothe plastic used for wrapping food has a ultraviolet ray resistanceeffect which prevents the food from being rotten or color-changing;however, it did not mention the effect to cyclic oligomer.

[0021] U.S. Pat. No. 5,744,572 discloses the addition of carboxyphosphonic acid catalyzes the reaction rate of polyester; however, itdid not mention the effect to cyclic oligomer.

[0022] The aforementioned prior arts did not mention the addition ofcalcium phosphate having Ca₃(PO₄)₂ or Ca₅OH(PO₄)₃ structure, or theaddition of phosphoric ester having structure (1), or the addition oftwo or more than two compounds simultaneously in order to restrain thecyclic oligomer content in PET chips and processed products thereof.

SUMMARY OF THIS INVENTION

[0023] The present invention discloses adding, during manufacturingprocess of PET chips, at least one selected from the group consisting ofcalcium phosphate having Ca₃(PO₄)₂ or Ca₅OH(PO₄)₃ structure and ofcarboxy phosphonic acid having a structure (1) as follows:

[0024] wherein R₁, R₂, and R₃ are alkyls or hydrogen atoms, R is analkyl;

[0025] the obtained PET chips and the manufactured product thereofcontain less cyclic oligomer than that of U.S. Pat. No. 6,392,005; theaddition of calcium phosphate or carboxy phosphonic acid havingstructure (I) into the polymerization reaction stage for manufacturingPET decreases the cyclic oligomer residuals in PET chips and effectivelyrestrains the regeneration of cyclic oligomer during processing.

[0026] The preferred embodiment of the present invention is that addingcalcium phosphate and compound having structure (1) simultaneouslyduring melt-polymerization reaction stage of manufacturing polyesterchips, the obtained polyester and product thereof contain less cyclicoligomer content than that of U.S. Pat. No. 6,392,005.

[0027] The most preferred embodiment of the present invention is thatadding calcium phosphate and compound having structure (1) and the PIcompound disclosed in our U.S. Pat. No. 6,392,005, the cyclic oligomercontent in the obtained PET chips and processed product thereof can befurther decreased; particularly, using the skill disclosed by thepresent invention appropriately decreases the addition amount of PIdisclosed in U.S. Pat. No. 6,392,005, which has an advantage of lowercost.

DETAILED DESCRITION OF THIS INVENTION AND THE PREFERRED EMBODIMENTS

[0028] The PET of the present invention can be obtained from thesynthesis of PTA process in which purified terephthalic acid andethylene glycol proceed with direct esterification and then meltedpolymerization, or from the synthesis of DMT process in which dimethylterephthalate and ethylene glycol proceed with transesterification andthen melted polymerization. The viscosity of PET obtained from each ofsaid processes is further increased to an appropriate level by solidstate polymerization. The PTA process is preferable for the presentinvention.

[0029] The present invention adds, before completion of the meltingpolymerization reaction of synthesizing PET, at least one selected fromthe group consisting of calcium phosphate having Ca₃(PO₄)₂ orCa₅OH(PO₄)₃ structure and of carboxy phosphonic acid having a structure(1) as follows:

[0030] wherein R₁, R₂, and R₃ are alkyls or hydrogen atoms, R is analkyl;

[0031] The calcium phosphate and carboxy phosphonic acid compound of thepresent invention can be injected into the slurry of PTA and EG, or beinjected during esterification stage, or be injected duringpolymerization reaction stage.

[0032] While adding calcium phosphate without the addition of carboxyphosphonic acid compound having structure (1) and the PI compound ofU.S. Pat. No. 6,392,005, the amount of added calcium phosphate is morepreferably 50˜500 ppm based on the weight of PET polymer, mostpreferably 100˜450 ppm based on the weight of PET polymer.

[0033] While adding the compound having structure (1) without theaddition of calcium phosphate and the PI compound of U.S. Pat. No.6,392,005, the amount of added compound having structure (I) is morepreferably 100˜700 ppm based on the weight of PET polymer, mostpreferably 100˜400 ppm based on the weight of PET polymer.

[0034] While adding calcium phosphate, compound having structure (1),and the PI compound of U.S. Pat. No. 6,392,005 simultaneously, the morepreferable composition is: the amount of added calcium phosphate ispreferably 100˜300 ppm based on the weight of PET polymer, the amount ofadded carboxy phosphonic acid compound having structure (1) ispreferably 100˜200 ppm based on the weight of PET polymer, and theamount of added PI compound is preferably 100˜500 ppm based on theweight of PET polymer.

[0035] The compound of Ca₃(PO₄)₂ of calcium phosphate used in thepresent invention has better effect on restraining the production ofcyclic oligomer.

[0036] The compound having structure (1) of the present invention ispreferably a compound called triethyl phosphonoacetate (hereinafterreferred to as TEPA) having a structure (2) as follows:

[0037] Based on the requirement of product application of the presentinvention, a heat stabilizer, a toner or a dye, a ultraviolet rayabsorbent, a crystallization accelerator, a static electricitypreventer, an oxidization resistant or a lubricant can be added.

[0038] The catalyst for PET of the present invention is antimonycatalyst such as antimony trioxide, or antimony acetate, the antimonycontent being no more than 300 ppm based on the weight of PET, or isgermanium dioxide catalyst having the germanium content being no morethan 100 ppm, or is titanium catalyst having the titanium content beingno more than 10 ppm based on the weight of PET.

[0039] The PET of the present invention can be either homogeneouspolymer or copolymer, adding dicarboxylic acid or diol compound such asdiethylene glycol (DEG), isophthalic acid (IPA), 2,6-naphthalenedicarboxylic acid, and cyclohexane dimethanol (CHDM).

[0040] The PET of the present invention is first manufactured to chipswith intrinsic viscosity of 0.45˜0.65 dl/g by melted statepolymerization, more preferably 0.57˜0.63 dl/g; then, the intrinsicviscosity of which is increased to above 0.70 by solid statepolymerization. The solid state polymerization can utilize stir-batchtype of operation at vacuum environment or utilize continuous tower tankthrough which an inert gas such as nitrogen gas or carbon dioxide isled.

[0041] The present invention accomplishes further decreasing andrestraining the cyclic oligomer content in PET chips and in theprocessed production thereof by adding at least one selected from thegroup consisting of calcium phosphate having Ca₃(PO₄)₂ or Ca₅OH(PO₄)₃structure and of carboxy phosphonic acid compound having structure (1).

EXAMPLES

[0042] The PET of the present invention, after solid statepolymerization to the level of preset intrinsic viscosity, is analyzedthe residual cyclic oligomer content.

[0043] The PET of the present invention is manufactured, by an injectorwith model of ASB 50H, into bottle embryo which is then analyzed thecyclic oligomer regenerated from melting process.

[0044] The method of analyzing cyclic oligomer for the present inventionis as follows: Accurately weighing 1000 grams of sample. Dissolving thesample into a transparent solution by hexafluoro-isopropanol solvent.Filtering the solution. The filtrate is then evaporated to obtain whitecrystallized powder of cyclic oligomer. The obtained white powder isdissolved into a transparent solution by dioxane and then analyzed by ahigh efficient liquid chromatographer to measure the respective contentof cyclic trimer, cyclic tetramer, cyclic pentamer, cyclic hexamer,cyclic heptamer, wherein mainly the cyclic trimer. The content of cyclicoligomer is the summation of said cyclic tri-, tetra-, penta-, hexa-,hepta-mers.

Example 1

[0045] Taking PTA and EG as raw materials. The quantity of PTA is 10.38kg. The added mole ratio of EG/PTA is 1.5. Blending into slurry andadding phosphoric acid with an amount of 140 ppm based on the weight ofpolymer. Raising the temperature up to 200° C.˜250° C. Proceeding withesterification for 4 hours under reaction pressure of 1.5˜2.0 Kg/cm².While the esterification ratio has reached over 95%, adding PI compound(Brand name: Irganox-1425, source: Ciba Corp.), calcium phosphateCa₃(PO₄)₂, and germanium dioxide catalyst respectively, the amount ofadded Irganox-1425 being 1000 ppm based on the weight of polymer, theamount of added Ca₃(PO₄)₂ being 200 ppm based on the weight of polymer,and the amount of added germanium dioxide catalyst being 140 ppm basedon the weight of polymer. After the addition of aforementionedadditives, vacuum polymerization reaction is proceeded. The first stagepolymerization reaction takes one hour, reaction pressure decreasingfrom normal pressure down to 10 torr, reaction temperature being 250°C.˜270° C. The second stage polymerization reaction decreases the vacuumintensity down to below 1 torr, reaction temperature being 270° C.˜285°C., stirring speed decreasing gradually along with the raising ofviscosity. The reaction stops when the intrinsic viscosity reaches 0.60dl/g, the polymer being unloaded to cooling water tank and cut intocolumn shape raw polyester chips by cutting machine.

[0046] Said raw chips are loaded in a twin-awl revolving vacuum dryingtank. Vacuum intensity in the tank is about 1 torr. The polyester chipsare heated by the following steps: first, 130° C. for two hours, thenraising the temperature to 180° C. and crystallizing for three hours,then raising the heating temperature to 230° C. and while the materialtemperature reaches 200° C., maintaining this temperature for 20 hours,then cooling down immediately so as to obtain the PET chips of thepresent invention. Analyzing their intrinsic viscosity and cyclictrimmer content thereof.

[0047] Said chips are manufactured into bottles of 2 litters by ASB-50inject-blow-molding machine; cyclic trimmer content of bottles isanalyzed.

[0048] Analyzed results are listed in Table 1, wherein the amounts ofadded additives are all calculated based on the weight of polymer.

Example 2

[0049] Process is the same as that of Example 1, however, only addingcalcium phosphate Ca₃(PO₄)₂ in an amount of 450 ppm based on the weightof polymer, and without the addition of PI compound and carboxyphosphonic acid having structure (1).

[0050] After solid phase polymerization reaction and inject-blow-moldingas Example 1, the results are listed in Table 1.

Example 3

[0051] Process is the same as that of Example 1, however, only adding PIcompound Irganox-1425 in an amount of 1000 ppm and carboxy phosphonicacid having structure (1) (TEPA) in an amount of 150 ppm, and withoutthe addition of calcium phosphate.

[0052] After solid phase polymerization reaction and inject-blow-moldingas Example 1, the results are listed in Table 1.

Example 4

[0053] Process is the same as that of Example 1, however, only adding PIcompound Irganox-1425 in an amount of 500 ppm and calcium phosphateCa₃(PO₄)₂ in an amount of 350 ppm, and without the addition of carboxyphosphonic acid having structure (1).

[0054] After solid phase polymerization reaction and inject-blow-moldingas Example 1, the results are listed in Table 1.

Example 5

[0055] Process is the same as that of Example 1, however, adding PIcompound Irganox-1425 in an amount of 500 ppm, calcium phosphateCa₃(PO₄)₂ in an amount of 300 ppm, and carboxy phosphonic acid havingstructure (1)(TEPA) in an amount of 150 ppm.

[0056] After solid phase polymerization reaction and inject-blow-moldingas Example 1, the results are listed in Table 1.

Example 6

[0057] Process is the same as that of Example 1, however, only adding PIcompound Irganox-1425 in an amount of 500 ppm and calcium phosphateCa₅OH(PO₄)₃ in an amount of 300 ppm, and without the addition of carboxyphosphonic acid having structure (1).

[0058] After solid phase polymerization reaction and inject-blow-moldingas Example 1, the results are listed in Table 1.

Comparative Example 1

[0059] Process is the same as that of Example 1, however, without addingPI compound, calcium phosphate, and carboxy phosphonic acid havingstructure (1).

[0060] After solid phase polymerization reaction and inject-blow-moldingas Example 1, the results are listed in Table 1.

Comparative Example 2

[0061] Process is the same as that of Example 1, however, only adding PIcompound in an amount of 1000 ppm, and without the addition of calciumphosphate, and carboxy phosphonic acid having structure (1).

[0062] After solid phase polymerization reaction and inject-blow-moldingas Example 1, the results are listed in Table 1. TABLE 1 Item additivesCyclic Cyclic Compound** Chips oligomer oligomer PI Calcium havingIntrinsic content in content in Example compound* phosphate structure(1) viscosity chips bottles Example 1 1000 ppm 200 ppm  0 ppm 0.78 0.5530.603 I-1425 Ca₃(PO₄)₂ Example 2   0 ppm 450 ppm  0 ppm 0.76 0.436 0.536Ca₃(PO₄)₂ Example 3 1000 ppm  0 ppm 150 ppm 0.80 0.429 0.533 I-1425 TEPAExample 4  500 ppm 350 ppm  0 ppm 0.78 0.441 0.512 I-1425 Ca₃(PO₄)₂Example 5  500 ppm 300 ppm 150 ppm 0.76 0.392 0.473 I-1425 Ca₃(PO₄)₂TEPA Example 6  500 ppm 300 ppm  0 ppm 0.76 0.467 0.553 I-1425Ca₅OH(PO₄)₃ Comparative   0 ppm  0 ppm  0 ppm 0.79 0.657 0.777 example 1Comparative 1000 ppm  0 ppm  0 ppm 0.81 0.592 0.679 example 2 I-1425

What is claimed is:
 1. A method for decreasing cyclic oligomer contentin polyester products comprising: adding, during the manufacturingprocess of polyethylene terephthalate, calcium phosphate at least oneselected from the group consisting Ca₃(PO₄)₂ and Ca₅OH(PO₄)₃ and carboxyphosphonic acid having the following structure (1):

; wherein R₁, R₂, and R₃ are alkyls or hydrogen atoms and R is an alkyl.2. The method for decreasing cyclic oligomer content in polyesterproducts during the manufacturing process of polyethylene terephthalateaccording to claim 1, wherein the amount of added calcium phosphate is50˜500 ppm based on the weight of PET polymer, and the amount of addedstructure (1) compound is 100˜700 ppm based on the weight of PETpolymer.
 3. A method for decreasing the cyclic oligomer content inpolyester products according to claim 2, wherein the intrinsic viscosityof the obtained PET chips is increased up to above 0.70 dl/g after solidphase polymerization.
 4. A method for decreasing the cyclic oligomercontent in polyester products according to claim 2, wherein apoly-condensation catalyst used during melting of the polyethyleneterephthalate can be selected from a group consisting of antimonycatalyst; germanium catalyst and titanium catalyst.
 5. Thepoly-condensation catalyst according to claim 4, wherein said antimonycatalyst is selected from a group consisting of antimony trioxide andantimony acetate, said germanium catalyst is selected from a groupconsisting of germanium dioxide, tetraethyl germanium oxide andn-tetrabutyl germanium oxide, and said titanium catalyst is tetrabutyltitanium oxide.
 6. The manufacturing method according to claim 2,wherein bottle embryos are made from polyester chips derived from saidmethod using an injection machine.
 7. The manufacturing method accordingto claim 6, wherein bottles are made from said embryos throughstretch-blow-molding.
 8. A method for decreasing cyclic oligomer contentin polyester products comprising: adding, during the manufacturingprocess of polyethylene terephthalate, calcium phosphate, PI and carboxyphosphonic acid having the following structure (1):

; wherein R₁, R₂, and R₃ are alkyls or hydrogen atoms and R is an alkyland said PI compound having the following structure (P1):


9. The method for decreasing cyclic oligomer content in polyesterproducts during the manufacturing process of polyethylene terephthalateaccording to claim 8, wherein the amount of added calcium phosphate is100˜300 ppm based on the weight of PET polymer, the amount of addedcarboxy phosphonic acid having structure (I) compound is 100˜200 ppmbased on the weight of PET polymer, and the amount of added PI compoundhaving structure PI is 100˜500 ppm based on the weight of PET polymer.10. A method for decreasing the cyclic oligomer content in polyesterproducts according to claim 9, wherein the intrinsic viscosity of theobtained PET chips is increased up to above 0.70 dl/g after solid phasepolymerization.
 11. A method for decreasing the cyclic oligomer contentin polyester products according to claim 9, wherein a poly-condensationcatalyst used during melting of the polyethylene terephthalate can beselected from a group consisting of antimony catalyst, germaniumcatalyst and of titanium catalyst.
 12. The poly-condensation catalystaccording to claim 11, wherein said antimony catalyst is selected from agroup consisting of antimony trioxide and antimony acetate, saidgermanium catalyst is selected from a group consisting of germaniumdioxide, tetraethyl germanium oxide and n-tetrabutyl germanium oxide,and said titanium catalyst is tetrabutyl titanium oxide.
 13. Themanufacturing method according to claim 9, wherein bottle embryos aremade from polyester chips derived from said method using an injectionmachine.
 14. The manufacturing method according to claim 13, whereinbottles are made from said embryos through stretch-blow-molding.